Aim of the piece is to give an introduction to basic differences between qualitative and quantitative approaches, named here as two schools of methods. Decision to take either quantitative or qualitative approaches, or a mix of both, is required for all researchers at all instances in the methodological decision making process. The article outlines, on which line methods can be distinguished. A structure of three types of methods is assumed, to which all given arguments are applied: Method of theory building, method of data generation, and method of data analysis. It will be revealed, to which extent qualitative or quantitative approach can contribute with reference to these types. At the end four general rules are presented as recommendation to be applied for method finding and method application of all method schools and types.